FORM2
THE PATENTS ACT, 1970
(39 of 1970)
&
The Patents Rules, 2003
COMPLETE SPECIFICATION
(See section 10; rule 13)
1. Title of the invention. - IMPROVED MECHANISM FOR CIRCUIT BREAKERS
2. Applicant(s)

(a) NAME : LARSEN & TOUBRO LIMITED
(b) NATIONALITY: An Indian Company.
(c) ADDRESS: L & T House, Ballard Estate, Mumbai 400 001,
State of Maharashtra, India
3. PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the invention and the manner in which it is to be performed:

TECHNICAL FIELD OF THE INVENTION
The present invention relates generally to a circuit breaker. More particularly, the invention relates to an improved mechanism for Moulded case circuit breakers.
BACKGROUND AND THE PRIOR ART
Circuit Breaker is a mechanical switching device capable of making, carrying and breaking currents. Under normal circuit conditions it will make the circuit closed, carry current for a specified time and breaks the circuit under specified abnormal circuit conditions.
Moulded Case Circuit Breakers (MCCB) is employed for current interruption. More particularly MCCBs are utilized to protect instruments from damage during adverse conditions prevailing during the operation of the circuit in which moulded case circuit breaker is employed.
During adverse conditions like short circuit, the current rises to an alarmingly high level. This high current may cause damage to the parts in the electrical system. Hence during these conditions the circuit has to be opened to protect the parts after the breaker.
A circuit breaker can be manually opened and closed, as well as automatically opened to protect conductors or equipments from damage caused by excessive heating due to over current in abnormal conditions such as overload or short-circuit.
The mechanism of the circuit breaker plays a vital role in determining the credibility of the breaker. A good mechanism should ensure quick and manually independent

opening and closing of contact system. Five operations are to be performed by the
MCCB mechanism.
They are:
1. ON
2. OFF
3. TRIP
4. TRIP FREE
5. RESET
The first two operations are initiated by operator whereas the trip signal is given by the release which senses the abnormal conditions and gives TRIP command to the mechanism, so that the latter opens the circuit.
The operator has access to the mechanism through the knob which will be projected outwards from the housing of the breaker. The knob is placed over the knob pin of the operating mechanism, which slides in the slot provided in the side plate. In conventional type MCCBs, breaker will feature three positions in the top cover near the knob to show ON, OFF and TRIP.
When the knob indicates ON it means the breaker is in ON condition i.e., the current path is closed. Similarly the position of the knob indicates the state of the circuit
breaker.
According to standards, the top position of the knob (if the breaker is placed vertically) or the longest distant position of the knob away from the operator (if the breaker is mounted horizontally) should be marked as ON POSITION. The other extreme end in both cases is marked as the OFF POSITION. The knob is substantially near the center (based on the design of the mechanism) to indicate the TRIP POSITION.

As discussed above, TRIP command is given automatically to the contacts by the release if it senses an abnormal condition like overload and short circuit. If the trip signal is given, the breaker opens the circuit and the knob goes to the trip position to show the operator that a fault has occurred in the system.
If the operator wants to switch ON the breaker after the breaker is tripped, he/she cannot do it without resetting the breaker. This is to make sure that the operator shouldn't switch ON the breaker before clearing the fault.
Resetting of the breaker is done by moving the knob towards the OFF position from the TRIP position. This movement loads the mechanism spring and now it is possible for the operator to ON the breaker.
All these mechanisms are called semi-automatic mechanisms since for ON and OFF operation, the knob of the breaker has to be taken from their respective ON or OFF positions to a position called dead center beyond which the mechanism becomes independent of the operator and completes the respective action by its own automatically.
US 5369384 disclose the breaker mechanism for power circuit breakers is the energy storage link between the handle and the contact systems. Known breaker mechanisms are generally too expensive to manufacture. When contact welding occurs, there is also the risk that, in spite of the tripping of the breaker mechanism, the contact system will not open. The new breaker mechanism reliably opens the contact system and consists of fewer and technologically simpler individual parts. It is inserted between two symmetrical breaker plates held in a die cast housing, and in which a connecting piece is mounted. Two toggle levers are connected at a distance from one another by means of a connecting shaft engaged in crossbar cam slots.

The drawbacks of the above mentioned prior art is that due to friction between moving parts and pins, we have to optimize the knob force & trip force for an instant as per standards and low mechanical advantage between spring and knob force.
Thus there is a need to provide a circuit breaker with roller based system which has much higher opening velocity than the existing mechanism, thus increasing the life of the breaker by reducing the fault clearing time and also opening of the contacts at normal time. The arrangement reduces the total trip time of the breaker during the fault condition. The response time of the mechanism is higher; as a result it provides higher opening velocity, which defines the efficiency of the breaker. Also, the life of the breaker is increased.
OBJECTS OF THE INVENTION
A basic object of the present invention is to overcome the disadvantages/drawbacks of the known art.
Other object of the present invention is to provide an improved mechanism for moulded case circuit breakers with roller based system with response time of the mechanism is higher adapted to have higher opening velocity.
Other object of the present invention is to provide an improved mechanism for moulded case circuit breakers with an arrangement reduces the total trip time of the breaker during the fault condition.
Yet another object of the present invention is to provide an improved mechanism for moulded case circuit breakers

These and other advantages of the present invention will become readily apparent from the following detailed description read in conjunction with the accompanying
drawings.
SUMMARY OF THE INVENTION
There is provided an improved mechanism for a circuit breaker.
According to one embodiment of the present invention, there is provided an improved mechanism for a circuit breaker comprising a knob attached to a knob pin sliding in a slot provided in a side plate; a latch link hinged to a side plate using a latch link pin, said latch link stopped in trip position using said knob pin; an operating link connected to said latch link using a rivet pin; a drive link connected to side plate using a connecting pin, said drive link having a pair of pin connector; a main spring connected between said knob pin and a spring pin; a trip system comprising a latch bracket holding a latch link using a latch bracket pin.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
In the appended drawings:
Figure 1 illustrates Isometric view of mechanism.
Figure 2 illustrates Exploded view of Mechanism.
Figure 3 illustrates ON POSITION.
Figure 4 illustrates OFF POSITION.
Figure 5 illustrates TRIP POSITION.

DETAILED DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The following drawings are illustrative of particular examples for enabling methods of the present invention, are descriptive of some of the methods, and are not intended to limit the scope of the invention. The drawings are not to scale (unless so stated) and are intended for use in conjunction with the explanations in the following detailed description.
Reference is first invited to Fig 1 where the improved mechanism for circuit breaker is shown. It shows isometric view of the mechanism.
Fig. 2 shows different components used in the mechanism. It shows a knob (5), knob pin (7), side plate (1), latch link (2), latch link pin 11 etc.
Fig. 3, 4 and 5 shows ON, OFF and TRIP position of the mechanism respectively.
The invented system is thus an improved mechanism for a circuit breaker.
DETAILED DESCRIPTION OF THE INVENTION
Accordingly the present invention has a knob 5 attached to the knob pin 7, which slides in the slot provided in the side plate. The knob pin 7 is used to stop the latch link 2 in the trip position and to reset the mechanism back to the OFF position as indicated in Fig. 4. The latch link 2 hinged to the side plates 1 with the help of latch link pin 11.
The operating links 3 are connected to the latch link 2 with the help of rivet pin 12. The orientation and position of the operating links 3 and drive links 4 are maintained by the presence of spring pin 15. The drive links 4 are connected to the side plate 1 by

using connecting pin 16. The drive link 4 has provided with two pin connector pins 13, which act as a roller for operating the mechanism to perform its operation.
The main springs are connected between the knob pin 7 and spring pin 15 through which the transmission of energy occurs from knob 5 to pin connector 13. The operating link 3 and the drive links 4 which performs the operations meant for an MCCB through pin connector 13. The pin connector 13 which in turn rotates the cassette
The latch bracket 6 which hold the latch link 2 in position by means of latch bracket pin 9 as shown in figs.3 & 4 in the ON & OFF conditions. During trip & trip free operations the trip signal will be given to the latch bracket 6 and as a result, the latching pin 10 is released enabling the latch link 2 to rotate about its pivot point. The components latch bracket pin 9, latch bracket 6, latching pin 10 comprises of the trip system.
ON position: ON position will be as shown in fig.3. In this position, the knob will be in the position far away from the trip system, the operating links 3, drive links 4 and pin connector 13 will be holding the contacts in the closed circuit condition
OFF position: OFF position will be as shown in fig.4. In this position, the knob will be in the position very near to the trip system the operating links 3, drive links 4 and pin connector 13 will be holding the contacts in the open circuit condition with the help of the drive shaft pin 9.
TRIP position: TRIP position will be as shown in fig.5. In this position, the knob will be in the position anywhere between the ON & OFF positions and the position is constrained by the rotation of latch link 2. The knob pin 7 stops the latch link 2 from further rotation. And the contacts will be in the opened condition.

Advantages:
• Less no of components in the assembly since only a set of operating links are used.
• High opening velocity by design.
• High mechanical advantage for knob force to main spring force.
• The roller based philosophy of the mechanism and the arrangement of the links in such a manner to suit to a circuit breaker, and thereby opening the contacts at a higher velocity to enhance the life of the circuit breaker ensuring trip free tristable condition which is a requirement as per standard.
• Since the spring length variation is very less compared to conventional mechanisms, the knob force required to operate the mechanism has reduced.
• Less friction between operating link and drive link.
Although the embodiments herein are described with various specific embodiments, it will be obvious for a person skilled in the art to practice the embodiments herein with modifications. However, all such modifications are deemed to be within the scope of the claims.
It is also to be understood that the following claims are intended to cover all of the generic and specific features of the embodiments described herein and all the statements of the scope of the embodiments which as a matter of language might be said to fall there between.

WE CLAIM:
1. An improved mechanism for a circuit breaker comprising:
a knob attached to a knob pin sliding in a slot provided in a side plate;
a latch link hinged to a side plate using a latch link pin, said latch link stopped in trip position using said knob pin;
an operating link connected to said latch link using a rivet pin;
a drive link connected to side plate using a connecting pin, said drive link having a pair of pin connector;
a main spring connected between said knob pin and a spring pin;
a trip system comprising a latch bracket holding a latch link using a latch bracket pin.
2. Mechanism as claimed in claim 1 wherein said circuit breaker is a moulded case circuit breaker.
3. Mechanism as claimed in claim 1 further comprising a spring loaded pin to maintain orientation and position of said operating link and said drive link.
4. Mechanism as claimed in claim 1 wherein said pair of pin connectors acting as rollers for operating said mechanism.

5. Mechanism as claimed in claim 1 wherein said main spring providing for energy transmission from said knob to said pin connector.
6. Mechanism as claimed in claim 1 wherein said operating link and said drive link performing operation through said pin connector.
7. An improved mechanism for a circuit breaker as herein described and illustrated with reference to the accompanying drawings.